Freeze-drying apparatus



sept. 6, 1966 Filed May 6. 1964 u. HAcKr-:NBERG ET AL 3,270,434

United States Patent O 3,270,434 FREEZE-DRYING APPARATUS Ulrich Hackenberg, Bensberg, Harald Kamps, Bruhl, and Helmut Rink, Bonn, Germany, assgnors to Leybold Anlagen Holding A.G., Zug, Switzerland Filed May 6, 1964, Ser. No. 365,533 Claims priority, application Germany, May 10, 1963, L 44,856 20 Claims. (Cl. .S4-92) This invention relates to 4freeze drying apparatus and more particularly to freeze dry-ing apparatus in which both the freezing and drying operations are performed in a single chamber.

Freeze drying is a well-known process in which a material to be dried is first fr-ozen and then placed inside an evacuable chamber. Water vapor removal apparatus, such as, for example, a deep-cooled ice condenser, then absorbs sublimating water vapor produced by heating of the frozen material. A predetermined low pressure is continuously maintained within the vacuum chamber during the drying process by means of conventional vacuum pumps communicating with the chamber.

One method of freezing materials to be dried entails subjecting the materials to a circulating stream of air which is cooled by a condenser device. The same condenser device is then frequently utilized to condense the water vapor sublimating from the material during the drying process. In the interest of reduced construct-ion material costs, the condenser 4device is sometimes located directly in the drying chamber itself. Such arrangements are particularly suitable in pharmaceutical freeze drying installations since the problems associated with the stringent sterilization requirements are simplified. However such arrangements have the disadvantage of expos-ing the condenser -device to radiators from the heaters required during the drying process thereby substantially reducing the efficiency of the condenser. It is therefore normally required to utilize radiation shields between the condenser elements and both the heating elements and the material being dried.

Another problem in freeze -drying installations which utilize drying chamber enclosed condenser elements is obtaining maximum pumping eficiency and compatibility between the condenser elements and the vacuum pumps required to remove non-condensable gases during the drying process. The water vapor pumping efciency of a condenser is much greater than that of conventional vacuum pumps. It is therefore desirable to remove as much of water vapor as possible with the condenser elements so as to reduce the pumping load of the vacuum pumps. In installations which utilize a separate housing for the condenser elements, this efficiency is accomplished by placing the condenser housing directly in series between the drying chamber and the vacuum pumps thereby insuring that all gas leaving the drying chamber will pass the condenser elements. In this Way substantially all the water vapor included in the pumped gas will be condensed in the condenser housing leaving only the relatively small quantity of non-condensable gas to be pumped by the vacuum pumps. To accomplish this result in an installation which positions the condenser elements directly in .the drying chamber is ya more difficult problem however.

An even m-ore serious drawback of the drying chamber enclosed condenser is that it renders impractical some of the drying process control methods commonly used in freeze drying installations. These methods require regulation of the conductance between the drying chamber and the pumping elements of the installation. Such conductance regulation is used, for example, to maintain certain material temperature and chamber pressure rela- 3,270,434 Patented Sept. 6, 1'966 ICC tionships in the interest of `a good quality product. This control met-hed is disclosed in U.S. Patent 3,077,036, Iissued February 12, 1963, to K. Neumann. It is also possible to determine the extent of material drying by completely isolating the drying chamber from the pumping elements and measuring the resulting pressure rise in the drying chamber. This method is disclosed in U.S. Patent 2,994,132, issued August 1, 1961, to the same K. Neumann. Inboth methods the conductance regulation is accomplished by positioning the condenser element in a separate housing and providing a valve device in the connecting tubulation between condenser housing an-d drying chamber.

The object of this invention is to provide a freeze drying instal-lation which exhibits the economy and advantages of a condenser element positioned -directly in the drying chamber but which also provides efficient, compatible use of the installations condenser :and vacuum pumps as well as allowing the regulation of conductance between the drying chamber and the condenser elements.

One feature of this invention is ya freeze drying` installation which provides a closed gas circulation path between a condenser element and the material being processed in a -drying chamber and which includes a valve mechanism permitting gas isolation of the condenser element from the material being dried.

Another feature of the invention is the provision of a freeze drying installation of the above-featured type wherein the closed gas circulation path is provided by an open ended housing positioned within the drying chamber and enclosing the material to be dried and the valve mechanism is adapted to close the open ends of the housing thereby isolating the material from the condenser device.

Another feature of the invention is the provision of a freeze drying installation of Ithe above-featured type including a valve operator which produces relative movement between the housing and the enclosing` vacuum chamber.

Another feature of the invention is the provision of a freeze drying installation of the above-featured type wherein the valve operator is adapted in one position to maintain both ends of the housing open providing a closed gas circulation path; in a second position` to close only one end of the housing providing an open gas evacuation path which passes the condenser element, yand in a third position to close both ends of the housing thereby isolating the material being drie-d from the condenser elements.

Another feature of this invention is the provision of a freeze drying instal-lation of the above-featured types wherein the isolating valve mechanism is also adapted to provide a radiant heat shield between material heating elements and the condenser device.

Another feature of this invention is the provision of a freeze drying installation of the above-featured type wherein the isolating valve mechanism comprises a pair of perpendicularly aligned, parallel plates each possessing gas circulation openings which are not in perpendicular alignment so `as to be closed upon surface contact of the parallel plates.

Another feature lof the present invention is the provision in freeze drying installati-ons of the above-featured types of a ventilator device for circulating gas through the enclosed housing.

The-se and other objects `and features of the present invention will become apparent upon `an examination of the following specification taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a longitudinal cross section taken through the freeze drying apparatus according to the present invention; and

FIG. 2 is a horizontal section partly in phanthom of the freeze drying apparatus shown in `FIG. 1 and showing the parallel plate valve mechanism of the present invention.

`Referring now to the drawings, there is shown the cylindrical evacuable chamber 1|1 having a centrally apertured 12 concave bottom portion 113. The open ended top portion of the evacuable chamber 1'1 terminates in a top flange 14 which supports the demountable cover plate 15. The annular -ange 16 of demountable cover l supports an operating handle 17 and possesses a hollow evacuation channel 18. Extending through an aperture 19 in the top flange 14 is the hollow evacuation tube 211 which is connected, as for example fby brazing, to the annular flange 16 in alignment with the hollow evacuation channel 18. The evacuation tube 21 is mounted for rotation in the chamber supported bracket 22 allowing the demountable cover 15 to rotate with the evacuation tube 21 to an open position. Extending in a gas tight manner through a central aperture in the cover plate 15 is the rotatable feed-through 23 which is connected to a fan 24. Aligned with another aperture in the cover plate 1-5 is the hollow tubulation 25 which connects to a pressure gauge 20.

Coaxially positioned within the evacuable chamber 11 is the open ended cylindrical housing 26 which divides the chamber 11 into the internal chamber portion 27 and the annular outer chamber portion 2S. The upper side of the housing 26 is partially closed by a cover plate 29 having a central aperture 31 adapted to accommodate the fan 24. The bottom end of the housing 26 is closed by the attached circular plate 32 which together with the housing 26 is supported by the central column 33. The operating lever 34 is fixed at one end to a rotary feedthrough 35 which extends through the wall of the evacuable chamber 11 and at its other end to the central column 33 so as to provide vertical movement thereof upon rotation of the rotary feed-through 35. The central column 33 is slidably contained tby the collar 36 which is supported from the concave chamber portion y13 by the support rod 37. Positioned below the circular plate 32 and having a plurality of horizontal turns is the hollow condenser coil 38 having an inlet 39 and an outlet 41 which extend in a gas tight manner through the evacuable chamber concave portion y13. Attached to the circular plate 32 and extending downwardly therefrom is the cylindrical auxiliary housing 42 which encloses the condenser coil 38 and has an open bottom end.

Within the housing 26 is the circular valve plate 43 which is supported from the concave chamber portion 113 by the support column 44. The support column 44 extends through a sufciently sized aperture in the circular plate 32 to allow relative movement therebetween. The circular valve plate 43 is directly above in perpendicular alignment With the circular plate 32 and is parallel thereto. The circular plate 32 contains four symmetrically placed apertures 45 and the circular valve plate 43 contains live symmetrically placed apertures 46 in addition to the annular opening 47 adjacent the housing 2'6. The annular opening `47 and the apertures 46 of the circular valve plate 43 are not in perpendicular alignment with the apertures 45 in the lower circular plate 32 so that upon surface contact of the plates all the openings in each plate will be closed by the opposing pla-te. This surface contact is provided by upward movement of the support column 63 and attached circular plate 32.

A pair of parallel spaced heating plates 51 are Supported by the vertical rod 52 which is attached to valve plate 43 by the nut 53. Electrical heating coils 54 in each of the heating plates 51 are connected to an electrical lead 55 within the support rod 512. Upon attachment of the vertical rod '52 to the valve plate 43, the electrical lead 55 makes contact with the electrical lead 56 which extends through support column 44, insulator 57, andan aperture in the concave chamber portion 13. A

carrying handle '58 is attached to the parallel heating plates 51.

'In the operation of the freeze drying installation, the closed evacuable chamber 11 is tirst sterilized by a quantity of steam directed into the chamber through the lower aperture 12. The steam is supplied `by a conventional steam producer (not shown) connected to the connecting flange `611. The steam supply device is then sealed from the chamber by a suitable valve mechanism (not shown). With the chamber interior sterilized the cover plates 15 and 31 are opened and the heating plate assembly 62 removed. A plurality of open llasks 63 filled with a material 64 to be freeze dried, such as for example a pharmaceutical product, a-re positioned on the lower heating plate .51. The heating plate assembly 62 is then lowered by the carrying handle 58 into the chamber internal portion 27 and attached with the holding nut 53. The cover plate 31 is then replaced and the cover plate 15 rotated into alignment with the top flange 14 and sealed thereto.

The freezing of the material 64 is begun with the housing 26 in its lowest position A. A supply of cooling fluid is circulated through the condenser coil 38 from a conventlonal cooling medium source (not shown) connected to the inlet 39 and outlet 41. Rotation of the fan 24 is started by a suitable driver (not shown) connected to the rotary feed-through 23. The rotating fan 2'4 causes air in the chamber 11 to circulate in a closed gas circulation path which passes the condenser coil B8 and the internal chamber portion 27 containing the product 64. This closed path extends from the interior of auxiliary housing 42 which encloses the condenser 38, through the apertures 45 in lower circular plate 32, through the apertures 46 and 47 in circular valve plate 43, through the internal chamber portion 27, out of the housing 26 through the rotating fan 24, `and down the external annular portion 28 to again enter the open end of the auxiliary housing 42. This closed circulation path provided by the divider housing -26 greatly reduces the time required to freeze the product y64 within the evacuable chamber 11.

On completion of the freezing process the fan 24 is de-energized and the housing 26 raised to its intermediate position B by upward movement of the central column 3'3. In this position the housing 26 will engage an annular sealing gasket attached to the annular flange 16 of cover plate 115. A suitable vacuum pump (not shown) connected to the rotatable evacuation tube 21 by a llexible vacuum line and vacuum valve ('both not shown) is then energized to reduce the pressure in the internal chamber portion 27 to a desired operating pressure of, for example, 10-1 millimeters of mercury. During this drying portion of the freeze drying process, water vapor sublimating from the frozen product 64 in the well known manner will be drawn lfrom the internal chamber portion 27 through apertures '45, 46, and 47 to be condensed on the condenser coil 38. Non-condensable gases mixed with the water vapor are pumped out of the open lower end of 4auxiliary housing 42, up the external annular portion 28, and out of hollow channel 18 and tubes 21 by the attached vacuum pump. Since all paths between the upper end of housing 26 and the vacuum line 21 have been closed by the sealing gasket 65, all removed gas must pass the condenser element 38 before reaching the evacuation line 21. This is a very desirable arrangement since substantially all condensable gas in the mixture will be condensed on the condenser coil 38 thereby substantially reducing the gas load on the connected vacuum pump.

When a degree of product dryness test is desired, the housing is raised to its top position C forming an additional seal between the housing 26 and the annular gasket 66. In this position the circular plate 32 is in surface contact with the valve plate 43 thereby sealing the openings 45, 46, and 47 and isolating the internal chamber portion 27 from the condenser and vacuum pumps. The resulting pressure rise inthe housing 26 will be indicated by the pressure gauge which is in gas communication therewith through the fan 24. This pressure rise indication can` then be used to determine the stage of the drying process. After the pressure rise has been noted, the housing is returned to position B and the drying proces continues in the manner describedy above.

Thus the present invention provides a freeze drying installation utilizing the economical placement of a condenser element directly in the freeze-drying vacuum chamber and still provides for isolation of the drying chamber from the condenser element so as to allow monitoring of the drying process by the rate of pressure rise method. The invention also provides with the housing 26 and the operator 34 av unique separator by which a closed gas circulation path between condenser element and drying product can be maintained during the freezing process and a condenser containing evacuation path provided for all pumped gases during the drying process thereby allowing efficient operation of the condenser elements and vacuum pumps.

Although the particular embodiment shown is preferred, many other designs and configurations could also prove effective. For example only, the chamber 11 could be positioned in other than a vertical position, the evacuable chamber 11 could be made movable and the housing 26 remain stationary to achieve the relative movement therebetween, the condenser coils 38 could be positioned partially or totally in the lannular external space 28, the heating plates 51 could be heated by other than electrical energy, thermal elements could be used to control the temperature of the heating plates 51, etc. It might also be desirable in certain installations, such as for example those in which the freeze drying of blood plasma or other pharmaceutical liquids is to be accomplished, to support the product carrying rack 62 from the rotary feed-through 23. This would allow rotation of the product iilled flasks 63 resulting in distribution of the liquid in thin layers on the walls of the flasks thereby allowing the liquid to freeze more quickly.

It is therefore to be understood that various modifications may be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter defined by the appended claims.

What is claimed is:

1. An apparatus for the freeze drying of moisture containing material including in combination:

(a) an evacuable chamber comprising,

a demountable portion adapted to provide access into said evacuable chamber, an evacuable chamber internal portion adapted to contain the material to be dried,

evacuation means adapted to permit evacuation of `said evacuable chamber,

heating means adapted to heat the material to be dried in said evacuable chamber internal portion,

condenser means positioned within said evacuable chamber and adapted to both freeze the material to be dried and condense moisture sublimating therefrom;

(b) divider means adapted to provide a closed gas circulation path between said condenser means and said evacuable chamber internal portion; and

(c) valve means having open and closed positions and adapted to isolate said condenser means from said evacuable chamber internal portion.

2. The apparatus according to claim 1 wherein said valve means is further adapted in both open and closed positions to substantially shield said condenser means from direct radiant heating by said heating means.

3. The apparatus according to claim `2 wherein said valve means comprises a pair of separable parallel plates in perpendicular alignment, means for providing relative be completely covered upon surface contact between said parallelk plates.

4. The apparatus according to claim 1 including gas moving means adapted to provide gas movement in said closed gas circulation path between said condenser means and said evacuable chamber internal'portion.

5. The apparatus according to claim 4 wherein said valve means is further adapted in both open and closed positions to substantially shield said condenser means from direct radiant heating by said heating means.

6. The apparatus according to claim 5 wherein said valve means comprises a pair of separable parallel plates in perpendicular alignment, means for providing. relative perpendicular movement between said parallel plates so as to produce surface contact therebetween, at least one aperture in` each of said parallel plates and wherein said apertures are not in perpendicular alignment so as to be cornpletely covered upon surface contact between said parallel plates.

7. The apparatus according to claim 1 wherein said divider means comprises an open ended housing means positioned within said evacuable chamber and enclosing said evacuable chamber internal portion, and said valve means is adapted to close the open ends of said housing to thereby isolate said evacuable chamber internal portion from said condenser means.

8. The apparatus according to claim 7 wherein said valve means includes a valve operator adapted to produce relative movement between said open ended housing and said evacuable chamber.

9. The apparatus according to claim 8 wherein said valve means includes at one end of said housing means a pair of separable parallel plates in perpendicular alignment, one of said parallel plates being supported by said evacuable chamber and one by said housing means so as to provide for relative movement and surface contact therebetween upon actuation of said valve operator, each of said parallel plates adapted to provide gas openings into said housing means and wherein said gas openings are not in perpendicular alignment so as to be completely covered upon surface contact between said parallel plates.

10. The apparatus according to claim 9 including sealing means adapted to seal closed the opposite end of said housing means upon movement of said parallel plates into surface contact.

11. Apparatus according to claim 10 including pressure measurement means adapted to measure the pressure in said evacuable chamber internal portion with said condenser means isolated therefrom.

12. The apparatus according to claim 11 wherein said housing means includes an open ended auxiliary housing portion which extends from that end of said housing means which includes said parallel plates and wherein said auxiliary housing portion encloses said condenser means.

13. An apparatus according to claim 12 including gas moving means adapted to provide gas movement through said housing means in said closed gas circulation path.

14. The apparatus according to claim 8 wherein said valve means is adapted, to provide openings at both ends of said housing means With said Valve operator in a first position, to close only one end of said housing means with said valve operator in a second position, and to close both ends of said housing means with said valve operator in a third position.

15. The apparatus according to claim 14 wherein said valve means includes at one end of said housing means a pair of separable parallel plates in perpendicular alignment, one of said parallel plates being supported by said evacuable chamber and one by said housing means so as to provide for relative perpendicular movement and surface contact therebetween in said third position of said valve operator, each of said parallel plates having an opening adapted to provide gas communication 'into said housing means with said valve operator in said first and second positions and wherein said openings are not in perpendicular alignment so as to be completely covered upon surface contact between said parallel plates.

16. The apparatus according to claim 15 including sealing means adapted to seal closed the opposite end of said housing means with said Valve operator in its second or third positions.

17. Apparatus according to claim 16 including pressure measurement means adapted to measure the pressure in said evacuable chamber internal portion with said condenser means isolated therefrom.

18. The apparatus according to claim 17 wherein said housing means includes an open ended auxiliary housing portion which extends from that end of said housing means which includes said parallel plates and wherein said auxiliary housing portion encloses said condenser means.

19. An apparatus for the freeze drying of moisture containing material including in combination:

' (a) an evacuable chamber comprising,

a demountable portion adapted to provide access into said evacuable chamber, evacuation means adapted to permit evacuation of said evacuable chamber,

an evacuable chamber internal portion adapted tov contain the material to be dried,

heating means adapted to heat the material to be dried Within said evacuable chamber internal portion,

said internal portion of said evacuable chamber and" said evacuation means pass directly by said condenser means.

20. The apparatus according to claim 19 including gas moving means adapted to circulate gas through said closed gas circulation path; and wherein said` separator' means comprises a divider housing means having two open ends and including one end portion enclosing said evacuable chamber internal portion and an opposite end portion enclosing said condenser means; said separator means further comprises an operator adapted to provide relative movement between said evacuable chamber and said housing means and to close the open end of said housing means end portion which encloses said evacuable chamber internal portion upon actuation of said operator.v

References Cited by the Examiner UNITED STATES PATENTS 2,564,475 8/1951 Fischer f 34-92 3,132,930 5/1964 Abbott 34-92 3,192,643 6/ 1965 Rieutord 3,4"92

WILLIAM J. WYE, Primary Examiner. 

1. AN APPARATUS FOR THE FREEZE DRYING OF MOISTURE CONTAINING MATERIAL INCLUDING IN COMBINATION: (A) AN EVACUABLE CHAMBER COMPRISING, A DEMOUNTABLE PORTION ADAPTED TO PROVIDE ACCESS INTO SAID EVACUABLE CHAMBER, AN EVACUABLE CHAMBER INTERNAL PORTION ADAPTED TO CONTAIN THE MATERIAL TO BE DRIED, EVACUATION MEANS ADAPTED TO PERMIT EVACUATION OF SAID EVACUABLE CHAMBER, HEATING MEANS ADAPTED TO HEAT THE MATERIAL TO BE DRIED IN SAID EVACUABLE CHAMBER INTERNAL PORTION, CONDENSER MEANS POSITIONED WITHIN SAID EVACUABLE CHAMBER AND ADAPTED TO BOTH FREEZE THE MATERIAL TO BE DRIED AND CONDENSE MOISTURE SUBLIMATING THEREFROM; (B) DIVIDER MEANS ADAPTED TO PROVIDE A CLOSED GAS CIRCULATION PATH BETWEEN SAID CONDENSER MEANS AND SAID EVACUABLE CHAMBER INTERNAL PORTION; AND 